Circuit breakers are special switches that are usually designed for high currents. These devices can not only switch operating currents and small overload currents, but also, in the event of faults, establish high overload currents and short circuit currents, maintain these fault currents for a specified time and interrupt them again. Circuit breakers are single-pole or multipole type depending on design.
Such circuit breakers generally incorporate so-called latches which, in the event of unwanted operating states, particularly short circuits, cause the circuit to be interrupted.
A latch is a mechanical device which preferably enables a circuit to be interrupted. For this purpose, to open the switching contacts, the force of a charged spring that has been charged via a tensioning mechanism on closure is usually released. The typical tripping criterion is a current of a predefinable magnitude whereby the locking is released by way of a solenoid or a bimetallic strip which becomes heated.
The latch of a circuit breaker has two essential regions. On the one hand, a switching mechanism is provided via which the opening and closing of an electrical switching contact is implemented subject to the spring force applied. On the other hand, such a latch has an unlatching mechanism which, when a tripping criterion is achieved, releases the energy stored in a spring of the switching mechanism, thereby tripping the latch and opening the electrical switching contact.
The problem with the latches known from the prior art is often that, in the locked state, the locking pawl provided inside the unlatching mechanism is brought into contact with a flat surface of the outer contour of the tensioning lever operatively connected to the spring. Since during operation of the circuit breaker the locking pawl thus comes into contact again and again with the same area of the locating surface of the tensioning lever, signs of wear become apparent the longer the breaker is in service. As a result of this abrasion of the locating surface, the direction of the normal force changes and therefore also the torque induced in the locating surface of the tensioning lever via the locking pawl. A higher torque in this area in turn causes the force required for tripping the latch to be increased.
Although it is possible to reduce the wear by employing harder materials or using a surface treatment process, this would increase the production costs of a corresponding component. Another possibility for reducing the locating surface abrasion is to implement a full surface lining between locking pawl and locating surface of the tensioning lever. The disadvantage of this, however, is that the lever arm of the normal force, i.e. the distance between the normal force vector and the force-inducing region of the locking pawl, can vary, which would result in fluctuations in the force required to trip the latch.